The 35,000 Dalton protein in brain supernatants that becomes labeled in the presence of nucleosides is glyceraldehyde-3-phosphate dehydrogenase. The labeled intermediate has been identified as the 3-phosphoglyceryl-S derivative of G3PDH. The precursor, glyceraldehyde-3-phosphate, is likely formed as the result of a series of reactions starting with nucleoside phosphorylase and phosphopentose mutase followed by the enzymes of the nonoxidative part of the pentose pathway. Protein kinase activity has been demonstrated in both the cortical and nuclear fractions of bovine lens. Histon II-AS and endogenous proteins can be phosphorylated. In the cortical fraction, a 51,000 band is phosphorylated. In the nuclear fraction, phosphorylated bands have molecular weights of 17,000-18,000, 20,000, 22,000, less than 10,000 and about 61,000. The first three are presumed to be subspecies of crystallins. Purified preparations of alpha-, beta-, and gamma-crystallins could not be phosphorylated by either the cortical or nuclear kinases or rabbit muscle cAMP-dependent protein kinases (peak I or peak II). The presence of phosphoserine or phosphothreonine could not be demonstrated in any of the crystallin preparations.